newschool72

iTrader: (12)

Little background, I have an LS3 crate engine in my 72 Camaro. Im running a custom grind cam (220-230 at .050 108+4, 629 lift), a GMPP dual plane carb intake, Fast EZ EFI, and hustler 1 7/8" long tubes.
I see where guys on here and in write ups say that the best timing for the rectangular port heads is right around 30* all in. The cutting edge combustion chambers are the reason for this low timing, because burning faster requires less lead for good flame travel.

My question is...Is the timing independent of the induction (intake) ? Most guys are running much higher timing with carb style intakes, 34 to 38*. Im running mine at 34* with a couple degree dip across the guesstimated torque peak. Ive been fighting a traction problem, so a good trip to the track hasn't happened yet. If my setup will make better average power at 29-30*, I will test some at that advance next time out. Retarding the timing might even help my traction issue, by killing a few ft lbs at lower RPMs.

So, anyone have any real insight as to whether the intake runner design will have any bearing on the combustion chambers ability to burn fuel ?

redtan

iTrader: (5)

Heck no, 30* is wayyy to much. These aren't SBCs, so that much timing is actually pretty high especially with a high DCR build that you're going to have with 104 ICL.

I would imagine no more than 24-26 depending on the gas.

I've never heard of LS3s running that much timing at WOT, and I don't think that the dual plane intake would change the way the cam and chambers work that you should run 10 more degrees. Maybe someone can prove me wrong, but most Gen IV LSx engines I've seen run in the mid 20s timing N/A.

newschool72

iTrader: (12)

If you go over to the carbed LSX forum, everyone is over 30* (almost) and some are pushing 36*-38*. These guys test at the track and get there best ETs and MPH at these settings! Thing is, I don't think they even start below 30*, but they pick up as the timing increases. I don't rely on the butt-o-meter often, but that's the only real way Ive been able to test with my traction issues at the track. My butt dyno says 34* feels stronger than 31*. In a 3500 lbs car, 3.42 gears, and a 2800 stall, my 72 Camaro has gone 11.65 at 118 with a 1.876 60 ft at 34*. If its 6-8* too high on timing, it has a good bit more in it, wouldn't you say?

redtan

iTrader: (5)

But you're not carbed tho right? You just have the dual plane intake with EFI?

Maybe a tuner can chime in as to why a dual plane intake LS3 with a pretty decent cam likes mid 30s timing.

newschool72

iTrader: (12)

Its an E-carb !LOL. Its the basic Fast EZ EFI with a 4 injector TB. The biggest difference in my setup and the carb guys is my screwdriver has a cord and buttons.

Dyno Junkie

Similar but not quite the same.

With EFI you have highly pressurised fuel in the rail which is released into the engine by the injector. The injector is told when to open by the ECU irrespective of what the engine needs.

With carburetors the fuel is sitting in their bowls and is drawn into the engine under vacuum. The vacuum is produced by the engine.

newschool72

iTrader: (12)

Well yea ! I fully understand the difference. My point is , its not sequential EFI. Its a batch fire setup, so it dumps fuel from the throttle body, just well atomized, instead of feeding individual cylinders like the factory style EFI most of you use. I like it because I have an ECU to communicate with the engine so I don't have all the carb tuning issues ( like on my old school 68 Camaro) AND I get the intake cooling effect ,at least to some point, that carbs enjoy.
Somebody come on here and give me some kind of proof, one way or the other, as to whether the engine timing would change because of the intake design. If I need to be at 28* with my LS3, then Im leaving a noticeable amount of power running at 34*. 5 or 6 degrees can add up to a tenth or better at the track. I can use that 10th or so to help me get to my goal with this car. Im recovering from a back surgery on Feb 26th, and wont be able to run the car for another 3 months or more and am using the time to pick this thing apart, LOL.

Bo White

iTrader: (59)

There are plenty of dynos in GA, see what it likes.

newschool72

iTrader: (12)

I don't have the funds to blow 150 bucks or more on a dyno day. I have nothing better to do than to hunt for some proof, one way or the other, on LS timing and its variables. I have 3 more months before the Dr will even let me get behind the wheel. Seems like this would be useful info for many , so lets figure it out.

Kip Fabre

Yes to your question. Your induction can affect the timing. Some my say no it can not. Here is how it can.
You have a Carb you run 36 degrees the next guy has a blower he runs 32. He pumps in more fuel/air it makes more presser and temperature which will need less timing. Once you get to a certain temperatures and presses you have detonation so less timing my be needed. The load has an effect so with a giver combination give it the timing it wants.
Not what you buddy has or what you want it’s what the engine wants. There are many other reasons that effect timing.

newschool72

iTrader: (12)

I can see a forced induction setup needing less timing , because VE goes out the roof when you cram the AF in the cylinder . I don't disagree , but the comparison of carbed vrs FI is almost a given that the FI engine will require less timing. In the case of different intakes we are still talking about 14.7 at sea level with both .
Anyone else have a contribution to go along with Kip. Kip, thanks for the thoughts on the subject.

DietCoke

iTrader: (18)

I'd run 30-32 and see how it acts. You will use more timing then a normal setup with that narrow lsa and style induction, but it's going to be sensitive to overtiming, too. As long as the engine isn't pinging, roll with it.